The invention relates to an electromechanically actuated disc brake having a self-boosting design.
Disc brakes, which reduce the power demand of the drive, by utilizing self-boosting effects have been known for a long time.
Typical examples of brakes of this type are described for example in DE 101 56 348 C1, in the slightly older, generic patent application DE 101 39 913.8, and in DE 10 2005 030 618.7.
Brakes of such design have in common the fact that the support of the tangential forces which act on the brake pad, takes place by way of a wedge or ramp system, which provides the self-boosting action.
Here, the friction force which acts on the brake pad is transmitted by a part, which is connected to the brake pad and which is movable with the latter in the tangential direction, of the self-boosting device via rolling bodies or by way of sliding contact against a part, which is stationary in the tangential direction, of the self-boosting device.
In disc brakes which do not have a self-boosting design and which have direct lever actuation, as described for example in DE 40 32 885 or WO 97/22 814, the actuating rams or plungers (or the bridge with plungers screwed therein) are guided with a narrow degree of play at least in the tangential direction. In DE 40 32 885, pivotably movable guidance of the bridge on the brake rotary lever is also provided.
The invention is initially based on the concept of utilizing a lever actuation, by way of a rotary lever, with a rotational axis which is orthogonal with respect to the brake disc rotational axis, for also applying a self-boosting disc brake.
In self-boosting disc brakes, however, a movement of the brake pad in the rotational direction of the brake disc is necessary to realize the self-boosting action.
In the case of actuating plungers which are guided in a movable or pivotable manner, this results in a relative movement between the brake pad or lining pressure plate and the actuating plunger(s).
Since high forces are transmitted via the contact point between the actuating plunger and the pressure plate both in the application and also in the retraction direction, the compensation of the relative movement requires suitable design measures.
In WO 03/07 1150 (Haldex), therefore, a self-boosting disc brake with a spindle drive, or with a direct rotationally actuated eccentric drive, has been described in which, to actuate the brake, the spacing between the bridge and the pressure plate is adjusted by a connecting rod which is driven by a crank. The connection of the connecting rod to the pressure plate permits a tangential movement of the brake pad and pressure plate by way of a pivoting movement of the connecting rod, with the other point of articulation of the connecting rod on the bridge remaining axially fixed. In this embodiment, the wear adjustment of the self-boosting disc brake takes place between the brake housing and the bridge.
In the lever-actuated brake, however, there is additionally a pivoting movement about the pivot axis, which is arranged in a crossing fashion, of the lever eccentric. Further difficulties arise from the necessity for the adjusting rotational movement to be introduced into the actuating plunger, which is pivotable about two mutually perpendicular axes.
Against this background, it is the object of the invention to make it possible, in a simple manner, for lever actuation to also be used for self-boosting disc brakes.
The invention achieves this, and other, objects by a self-boosting electromechanically actuable disc brake having a brake caliper, at least one application-side and one reaction-side brake pad, and a brake disc. An electromechanical drive and a brake application device for applying the brake pad are provided, which brake application device has a rotary lever and a self-boosting device. The rotary lever acts on a single-part or multi-part actuating plunger, which acts directly or via a pressure plate on the application-side brake pad. Preferably, at least one wear adjusting device for adjusting brake pad and/or disc wear is provided. The actuating plunger is pivotably mounted on the rotary lever and on the pressure plate or on the application-side brake pad.
According thereto, the actuating plunger is pivotably mounted on the rotary lever and on the pressure plate or on the application-side brake pad with a preferably intersecting rotational axis, which makes it possible, in a simple manner, for the concept of the rotary lever actuation to also be used for self-boosting disc brakes.
The actuating plunger is preferably pivotably fastened to the brake rotary lever and to the pressure plate or to the application-side brake pad in such a way that the actuating plunger can transmit tensile and compressive forces between the brake pad and its drive (for example an electric motor with a threaded drive).
The expression “actuating plunger” or “actuating ram” should not be interpreted in a narrow sense. The expression, in particular, also encompasses modules which are variable in length and which are composed of a plurality of elements.
For a directly lever-actuated self-boosting disc brake, therefore, a coupling of the actuating plunger to the pressure plate of the brake pad has been discovered, by which both application and retraction actuating forces and movements can be transmitted safely and reliably. The actuating plunger is particularly preferably mounted on and fastened to the eccentric rotational shaft of the rotary lever and to the pressure plate or to the application-side brake pad in such a way that the actuating plunger can compensate pivoting movements of the rotary lever and tangential sliding movements of the brake pad and, if appropriate, of the pressure plate by pivoting in the mutually perpendicular pivoting directions.
Therefore, with a small amount of required installation space, it is both the case that the tangential movement of the pressure plate, which is required to obtain the self-boosting action is enabled, and also that a compensation of the tilting movement of the actuating plunger is enabled on account of the purely rotationally movable guidance in the eccentric of the brake rotary lever.
The transmission of force takes place, here, both on the brake rotary lever side and also on the lining pressure plate side via joint journals, with the journal of the brake rotary lever being arranged such that its rotational axis intersects that of the lining pressure plate.
The actuating plunger unit is preferably fitted, at both mounting ends, with pivot bearings, for example plain spherical bearings.
Furthermore, according to one particularly advantageous refinement, the introduction of the adjusting rotational movement into the actuating plunger, which is pivotable in two directions, is enabled.
For this purpose, the actuating plunger is firstly designed as a module, which is axially variable in length, in particular telescopic, and which permits a change in length of the brake ram for compensating brake pad and/or disc wear.
The actuating plunger module is preferably composed of an actuating plunger, threaded spindle and joint bearing housing, and is coupled by way of a synchronization gearing to a wear adjusting device.
The actuating plunger unit composed of the actuating plunger, the threaded spindle and the joint bearing housing is particularly preferably connected in a structurally simple manner to a gearwheel in order to transmit the adjusting rotational movement.
Here, the gearwheel is preferably designed such that, when the brake is not actuated, that is to say in the rest position of the actuating plunger, there is a narrow degree of tooth play with respect to the further coupled gearwheels.
When the brake is actuated, however, the gearwheels are placed so far out of engagement by the application movement of the actuating plunger that the pivoting movement of the actuating plunger, which then takes place, is enabled.
Alternative embodiments are also possible for the joint bearings on the brake rotary lever eccentric rotational axle shaft and at the pressure plate connection of the actuating plunger.
It is, for example, also possible to use a pivotable spherical roller bearing on the brake rotary lever eccentric axle shaft. At the connecting point to the pressure plate, simpler solutions are also contemplated for compensating the pivoting movement, which results from the pivotably movable guidance on the brake rotary lever. Even a slightly spherical rotary axle may be sufficient, and/or a bearing bush which is flared slightly in terms of diameter toward the two end regions.
According to a further invention, which is also to be considered as independent, the stationary component of the self-boosting device, which stationary component is connected to the wear adjusting device, is preferably held, with a small degree of play, parallel to the brake disc rotational axis between guide surfaces of the axially fixed component of the brake. This is done in such a way that, during braking processes, the tangential forces which occur are transmitted, so as to be supported, directly from the stationary component of the self-boosting device to the axially fixed component of the brake.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.